It is now clearly established that specific scent glands and other biological odor sources are widespread throughout the animal kingdom, including primates and possibly humans. The available evidence indicates that olfactory stimuli from these natural sources can elicit specific behavioral responses or change the neuro-endocrine status of an organism. Moreover, components of a particular behavioral sequence may be elicited by different chemical species within a single melange of natural odors and also be critically dependent upon only a portion of the available sensory apparatus (i.e., either the main or accessory olfactory system). The range of animal behaviors which are modulated by the olfactory system includes those (e.g., mating behavior) that depend on the normal afferent signals in the system and those which seem to depend on the integrity of the central sensory apparatus but not on the afferent signals themselves (e.g., nest building). In addition, normal behavioral responses to natural odors are often modulated by endogenous hormone levels of both sender and recipient organisms. There are several broad questions to be answered about the mechanisms of olfactory communication in mammals, including: (1) How do natural scents activate the olfactory and vomeronasal organs? (2) Are there special modes of activation for behaviorally important odors, like pheromones; or are all odorants, regardless of origin or import, treated in the same way? (3) Once the system has been activated, are there distinctive coding mechanisms which operate in selected anatomical regions for particular classes of odorants? (4) What is the functional neuroanatomy of the olfactory and vomeronasal systems, especially with regard to those areas concerned with the perception of pheromones? (5) What are the relative contributions of olfactory and other sensory signals in modulating mating and other behaviors? The hamster will be the primary model because it has well-recognized sources of natural scent, several of which are partially characterized. It has specific scent-marking behaviors for the deposition of these scents and easily measured behavioral responses to their perception, all of which are under the control of endogenous hormones. In this project several investigators will direct their disparate backgrounds and diversified skills to studying the mechanisms of olfactory communication in mammals. C (Text Truncated - Exceeds Capacity)